1. Field of the Invention
The present invention relates to a narrow band rejection filter utilizing a liquid crystal cell and, more particularly, to a simple, inexpensive, and rapid technique for constructing a narrow band light rejection filter.
2. Description of the Prior Art
There are a variety of circumstances in optical instrumentation where one would like a narrow band rejection filter which will reject a single wavelength of light and pass either selected others or all others. For example, in fluorescence measurements, if a sample is excited by light of wavelength .lambda..sub.1, a fluorescing sample will emit light having a wavelength .lambda..sub.2. Since the wavelength of fluorescence is typically larger than the wavelength of excitation, it is common to use a low pass filter between the incoming light beam and the sample and a high pass filter between the sample and the detector. In order for the measurements to be accurate, there should be no overlap between the pass bands of the filters, but this is virtually impossible using conventional filter elements.
Raleigh scattering spectroscopy and Raman scattering spectroscopy present similar problems. In both, a sample is excited at a first wavelength and light is scattered at different wavelengths. In both types of spectroscopy, sharp separation filters are required. However, simple filters simply do not function in an adequate manner.